LCDs are widely used in various information products, such as notebooks, personal digital assistants, video cameras, and the like.
FIG. 4 is essentially an abbreviated circuit diagram of a conventional LCD. The LCD 100 includes a liquid crystal panel 101, a scanning circuit 102, and a data circuit 103. The liquid crystal panel 101 includes n rows of parallel scanning lines 110 (where n is a natural number), m columns of parallel data lines 120 perpendicularly to the scanning lines 110 (where m is also a natural number), and a plurality of pixel units 140 cooperatively defined by the crossing scanning lines 110 and data lines 120. The scanning lines 110 are electrically coupled to the scanning circuit 102, and the data lines 120 are electrically coupled to the data circuit 130.
Each pixel unit 140 includes a thin film transistor (TFT) 141, a pixel electrode 142, and a common electrode 143. A gate electrode of the TFT 141 is electrically coupled to a corresponding one of the scanning lines 110, and a source electrode of the TFT 141 is electrically coupled to a corresponding one of the data lines 120. Further, a drain electrode of the TFT 141 is electrically coupled to the pixel electrode 142. The common electrodes 143 of all the pixel units 140 are electrically coupled together and further electrically coupled to a common voltage generating circuit (not shown). In each pixel unit 140, liquid crystal molecules (not shown) are disposed between the pixel electrode 142 and the common electrode 143, so as to cooperatively form a liquid crystal capacitor 147.
In operation, the common electrodes 143 receive a common voltage signal from the common voltage generating circuit. The scanning circuit 102 provides a plurality of scanning signals to the scanning lines 110 sequentially, so as to activate the pixel units 140 row by row. The data circuit 103 provides a plurality of data voltage signals to the pixel electrodes 142 of the activated pixel units 140. Thereby, the liquid crystal capacitors 147 of the activated pixel units 140 are charged. After the charging process, an electric field is generated between the pixel electrode 142 and the common electrode 143 in each pixel unit 140. The electric field drives the liquid crystal molecules to control light transmission of the pixel unit 140, such that the pixel unit 140 displays a particular color (red, green, or blue) having a corresponding gray level. The electric field is maintained by the liquid crystal capacitor 147 during a so-called current frame period, and accordingly the gray level of the color is maintained during the current frame period.
In the LCD 100, each pixel unit 140 employs a capacitor structure (i.e. the liquid crystal capacitor 147) to retain the gray level of the color. In addition, a plurality of parasitic capacitors usually exist in the pixel unit 140. Due to a so-called capacitor coupling effect, when the data voltage signal received by the pixel electrode 142 changes, an electrical potential of the common electrode 143 may be coupled and shift from the common voltage signal. Because the pixel units 140 are activated and receive the data voltage signals row by row, the electrical potentials of the common electrodes 143 of the activated row of pixel units 140 are liable to be pulled up or pulled down simultaneously and thereby have undesired values. Moreover, because the common electrodes 143 of the activated row of pixel units 140 are electrically coupled together, the undesired values of the electrical potentials are the same.
The shift of the electrical potential of the common electrode 143 may further bring on a change of the electric field between the pixel electrode 142 and the common electrode 143. Thereby, the gray level of the color displayed by the pixel unit 140 is apt to change, and accordingly a so-called color shift phenomenon may be generated. Thus the display quality of the LCD 100 may be somewhat unsatisfactory.
What is needed is to provide an LCD and a driving method thereof which can overcome the above-described deficiencies.